FIG. 1 depicts a schematic diagram of wireless network 100 in the prior art, which comprises wireless telecommunication terminal 101 and access points 102-1 through 102-L, interconnected as shown. Wireless terminal 101 uses access points 102-1 through 102-L to exchange blocks of data, or “packets,” with computer servers that are external to wireless network 100. At any given time, wireless terminal 101 is associated with one of access points 102-1 through 102-L for the purpose of communicating with the external servers.
It is important in some operating scenarios to know the location of wireless terminal 101 within wireless network 100. Knowing the location enables, for instance, services that use end-user location information. Such services include location-aware content delivery, emergency location, services based on the notion of “closest resource,” and location-based access control.
Various techniques for estimating location exist in the prior art. Although some prior art techniques perform well in some operating environments, there are other operating environments in which prior art techniques do not perform adequately. The example that follows highlights a shortcoming in prior art techniques. FIG. 2 depicts a schematic diagram of a cross-section of a building (e.g., an office complex, etc.). Access points 102-1 and 102-2 are situated on the first floor, access points 102-3 and 102-4 are situated on the second floor, and access points 102-5 and 102-6 are situated on the third floor.
In determining the location of wireless terminal 101 in FIG. 2, the problem is first determining the floor on which wireless terminal 101 is presently located. It has often been assumed in the prior art that determining the floor at which wireless terminal 101 is located should be straightforward, since a typical building floor in a multi-story environment significantly attenuates the signal from wireless terminal 101. Often, however, the signal from wireless terminal 101 can be received on more than one floor, as is the case in FIG. 2. The access points on multiple floors can receive a wireless terminal's signal in a variety of situations, such as where a building layout includes an atrium; where elevator shafts, stairwells, large ductwork, or escalators are present; etc. In these operating environments, it is sometimes the case that the floor receiving the strongest signal or the most signals is not the floor in which the wireless terminal is located.
What is needed is a technique to improve estimating the location of a wireless terminals across multiple building floors without some of the disadvantages of the prior art.